Many different processes and compositions have been proposed for reducing the nitrogen oxides concentration in an effluent. For instance, in U.S. Pat. No. 3,900,554, Lyon discloses reducing nitrogen monoxide (NO) in a combustion effluent with ammonia and specified ammonia precursors or their aqueous solutions, which are injected into the effluent for mixing with the nitrogen monoxide at a temperature within the range of 1600.degree. F. to 2000.degree. F.
In U.S. Pat. No. 3,961,018, Williamson discloses the purification of acid gas-containing streams at low temperatures approaching ambient by contacting the gas stream with an amine vapor in sufficient concentration such that its partial pressure is at least 5% of the total pressure of the gas stream.
In a somewhat different environment, Goldstein et al., in U.S. Pat. No. 4,061,597, indicate that temperatures within the range of 1000.degree. F. to 1300.degree. F. are effective when using urea for reducing brown fumes caused by nitrogen dioxide (NO.sub.2) from catalyst treatment effluents.
In U.S. Pat. No. 4,325,924, Arand et al. disclose that under fuel-rich conditions, aqueous solutions of urea at concentrations of greater than 10%, and preferably greater than 20%, are effective nitrogen oxide reducers at temperatures in excess of 1900.degree. F.
In U.S. Pat. No. 4,208,386 Arand et al. disclose that, for oxygen-rich effluents, the temperature is in the range of 1300.degree. F. to 2000.degree. F. for urea added dry or in aqueous solution. Alkanoic solvents are said to be reducing agents which, like hydrogen, carbon monoxide, etc., are said to enable the effective operating temperature to be lowered to below 1600.degree. F.
In improvements to these prior art processes, Bowers, in copending and commonly assigned U.S. patent application, Ser. No. 784,826, filed Oct. 4, 1985, and copending and commonly assigned U.S. patent application, Ser. No. 811,532, filed Dec. 20, 1985, discloses the use of a urea solution, which preferably also comprises hexamethylenetetramine, to reduce the NO.sub.x concentration in the effluent of a carbonaceous fuel. The application of urea in a dilute solution of medium to coarse particle size solution allows the effluent to be treated while at a higher temperature.
In a further variation, copending and commonly assigned U.S. patent application Ser. No. 784,828, filed Oct. 4, 1985, to Bowers, discloses injecting an aqueous urea solution containing an oxygenated hydrocarbon to control ammonia concentrations while reducing NO.sub.x in an effluent.
Although the art has provided compositions which are effective at reducing the NO.sub.x concentrations in an effluent while the effluent is still extremely hot, the method and apparatus for injecting the compositions into the effluent remains the subject of an intense search.
The problems facing the successful production of method and apparatus for injecting such compositions into an effluent are many. For instance, the extreme heat of the effluent will readily cause a loss in structural integrity of most nozzles or their supports; when the composition to be injected is a solution, often precipitated solute will collect at the end of the nozzle and can block or clog the nozzle or break off as chunks and damage the interior of the boiler; and the need for variability of droplet size and degree of dispersion when situations require, such as situations where the load of the boiler varies. These problems have not been successfully addressed by the prior art.
There exists a present need, therefore, for an apparatus and a process for injecting a treatment fluid, e.g., an aqueous solution of a NO.sub.x reducing composition into an effluent of the combustion of a carbonaceous fuel, allowing for independent variability of droplet size and spray parameters.